Learn Crafting System

Wonder Man gives you this quest, Learn Crafting System, in the north section of the Avenger Tower. He tasks you to collect 3 Simple Particles of a particular type, then return to him.

Simple Particles, like other crafting particles, are random drops on normal mobs. You'll need to mouse over the item to make sure they're Simple particles; "Unstable" or better won't work. At your low level, it's highly unlikely you'll find anything but simple particles anyway, but you will likely find other types. Simply going through the other missions will usually help lead you to find them; just defeat everyone you see, and collect the loot!

The specific type of particle you need for this quest, such as Pym Particles, is random. You'll likely find many particles of all the different types as you fight, and you'll need them all anyway.

Once you've got your particles, return to Wonder Man in the Avengers Tower to learn how precisely to craft. Once you make the sample recipe he wants you to make, you'll be done with this mission.

Remember that the best feature of the crafting system is that, during the process, your S.T.A.S.H. automatically opens, so you can simply store all your particles in there so you don't need to burden your inventory space with them.